Abstract

Quantifying ear-canal sound level in forward pressure has been suggested as a more accurate and practical alternative to sound pressure level (SPL)calibrations used in clinical settings. The mathematical isolation of forward (and reverse) pressure requires defining the Thévenin-equivalent impedance and pressure of the sound source and characteristic impedance of the load; however, the extent to which inaccuracies in characterizing the source and/or load impact forward pressure level (FPL) calibrations has not been specifically evaluated. This study examined how commercially available probe tips and estimates of characteristic impedance impact the calculation of forward and reverse pressure in a number of test cavities with dimensions chosen to reflect human ear-canal dimensions. Results demonstrate that FPL calibration, which has already been shown to be more accurate than in situSPLcalibration, can be improved particularly around standing-wave null frequencies by refining estimates of characteristic impedance. Better estimates allow FPL to be accurately calculated at least through 10 kHz using a variety of probe tips in test cavities of different sizes, suggesting that FPL calibration can be performed in ear canals of all sizes. Additionally, FPL calibration appears a reasonable option when quantifying the levels of extended high-frequency (10–18 kHz) stimuli.

Received 02 June 2011Revised 01 October 2011Accepted 04 October 2011Published online 15 December 2011

Acknowledgments:

This work was supported by Grant IRG-77-004-31 from the American Cancer Society, administered through the Holden Comprehensive Cancer Center at the University of Iowa and a 2010 Clinical Research Grant from the American Speech-Language-Hearing Foundation. The first author was supported by an NIH training grant (T32-D0073666). The authors thank James Lewis for helpful insights throughout data collection/analysis and individuals at AAS 2011 and the reviewers for their comments and suggestions.